Nielsen's just released a study confirming what some other studies have already concluded -- that Android devices account for the single largest swath of smartphone users in the US, with 39 percent OS share as of the second quarter. That compares with 28 percent for iOS, although Apple still reigns as the country's top-selling device maker. Simply put, that's a reflection of the fact that Apple is the only outfit churning out iOS devices, whereas a bevy of companies led by HTC, Motorola, and Samsung have helped make Android the dominant OS in the states. And let's not forget about RIM, another hardware / software shop, which still commands a 20 percent chunk of the market. Rounding out the list, Windows Phone and Windows Mobile account for nine percent, largely thanks to sales of HTC handsets, while webOS and Symbian each eked out two percent. At this point we don't doubt that Android is the most ubiquitous mobile operating system this side of the Atlantic, although it's worth noting that Nielsen based its results on a sample of roughly 20,000 people -- all of whom are postpaid subscribers.